Underpinning Contractors

The structural engineer chooses the method based on the depth of firm ground, the loads, the condition of the building and the access.

Underpinning is never done by digging out a whole wall at once. The engineer sets a sequence of short sections, often called "pins", which are dug in a hit-and-miss order: for example sections 1, 4 and 7 first, then 2, 5 and 8, then 3, 6 and 9. That way, most of the wall is always supported by the ground or by completed underpinning. Each section is inspected by building control before the concrete is poured.

Often only the part of the house that has moved, such as a corner, a bay or a rear addition, needs underpinning. But underpinning one part can create a difference in stiffness between the underpinned and non-underpinned sections, which can cause cracking at the junction. The engineer decides how far the underpinning must extend to avoid that.

To lower a cellar floor or dig a new basement, the walls above must be underpinned first, because the new floor will be below the existing foundations. Basement underpinning is usually reinforced concrete that also acts as a retaining wall, holding back the soil once the floor is dug out. It is sequenced in the same way, with temporary supports where needed. See our basement conversions service.

In terraced and semi-detached houses, almost always. Under the Party Wall etc. Act 1996:

• Underpinning a party wall needs a party structure notice, served at least two months before the work starts.
• Digging near a neighbour's building needs an adjacent excavation notice, served at least one month before, if you excavate within 3 metres and deeper than their foundations, or within 6 metres where the excavation would cut a line drawn at 45 degrees down from the bottom of their foundations.

Your neighbour can consent in writing, or dissent. If they dissent, a party wall surveyor, or one each, prepares a party wall award setting out how the work will be done and recording the condition of their property first. We plan the programme around the party wall process and follow the award.

Often, yes. Where the underpinning is dug from outside, most of the house stays usable, although there will be noise, dust and restricted access around the work. Where the work has to be done from inside, floors may need to be lifted and rooms emptied, and it may be easier to move out for part of the time. We explain what to expect at the survey.

Once the foundations are secure, the damage caused by the movement can be repaired properly:

• Crack stitching: Stainless steel bars bonded into the brickwork across larger cracks.
• Internal cracks: filling cracks in walls, fixing ceiling cracks and plaster patch repair.
• Doors and windows: Easing or refitting frames that had gone out of square.
• Drains: Repairing any damaged drains through our drain repairs and lining service.
• Decoration: painting to finish.